The ending, in which a janitor casually walks up to the remains of eponymous Incredible Melting Man, gathers them up, throws them into a nearby trash bin, and goes on about his day.
It's more dark comedy, but "Don't shoot! I'm Dr. Ted Nelson!" BLAM!
When you keep in mind a lot of stuff in the movie was written to be comedic, it's easy to see how it can still be rather funny. For example, instead of being a petite and sexy victim of the monster who trips on a Broken Heel, the nurse is a beefy, overweight woman who barrels straight through a hospital entrance and shatters it to pieces.